McCartney without Preston and All Things Must Pass

Listening to Billy Preston's strong version of My Sweet Lord from the 
"Concert for George" CD now, I really find it interesting that Paul has never 
employed Billy Preston over the years.  Ringo toured with him, and he not 
only toured with George but played on several of the solo LP's.

Considerng that Paul always has promoted the Beatles more than any of the ex-
Fabs, I wonder why Billy never played keys on any of his albums or solo 
tours.  I know that I would have a warm feeling seeing the two of them up 
there (Ringo would be nice, too Paul, if by some miracle this gets back to 
you).


By the way, did anyone catch that interview with Clapton where he said that 
Paul didn't know "All Things Must Pass" and that he had to learn it?
Did he mean that Paul never heard the song?!!!